The wild chili pepper Capsicum chacoense produces the spicy defense compounds known as capsaicinoids, including capsaicin and dihydrocapsaicin, which are antagonistic to the growth of fungal pathogens. Compared to other microbes, fungi isolated from infected seeds of C. chacoense possess much higher levels of tolerance of these spicy compounds, having their growth slowed but not entirely inhibited. Previous research has shown capsaicinoids inhibit microbes by disrupting ATP production by binding NADH dehydrogenase in the electron transport chain (ETC) and, thus, throttling oxidative phosphorylation (OXPHOS). Capsaicinoids may also disrupt cell membranes. Here, we investigate capsaicinoid tolerance in fungal seed pathogens isolated from C. chacoense. We selected 16 fungal isolates from four ascomycete genera (Alternaria, Colletotrichum, Fusarium, and Phomopsis). Using relative growth rate as a readout for tolerance, fungi were challenged with ETC inhibitors to infer whether fungi possess alternative respiratory enzymes and whether effects on the ETC fully explained inhibition by capsaicinoids. In all isolates, we found evidence for at least one alternative NADH dehydrogenase. In many isolates, we also found evidence for an alternative oxidase. These data suggest that wild-plant pathogens may be a rich source of alternative respiratory enzymes. We further demonstrate that these fungal isolates are capable of the breakdown of capsaicinoids. Finally, we determine that the OXPHOS theory may describe a weak primary mechanism by which dihydrocapsaicin, but not capsaicin, slows fungal growth. Our findings suggest that capsaicinoids likely disrupt membranes, in addition to energy poisoning, with implications for microbiology and human health.

IMPORTANCE Plants make chemical compounds to protect themselves. For example, chili peppers produce the spicy compound capsaicin to inhibit pathogen damage and animal feeding. In humans, capsaicin binds to a membrane channel protein, creating the sensation of heat, while in microbes, capsaicin limits energy production by binding respiratory enzymes. However, some data suggest that capsaicin also disrupts membranes. Here, we studied fungal pathogens (Alternaria, Colletotrichum, Fusarium, and Phomopsis) isolated from a wild chili pepper, Capsicum chacoense. By measuring growth rates in the presence of antibiotics with known respiratory targets, we inferred that wild-plant pathogens might be rich in alternative respiratory enzymes. A zone of clearance around the colonies, as well as liquid chromatography-mass spectrometry data, further indicated that these fungi can break down capsaicin. Finally, the total inhibitory effect of capsaicin was not fully explained by its effect on respiratory enzymes. Our findings lend credence to studies proposing that capsaicin may disrupt cell membranes, with implications for microbiology, as well as human health.

野生辣椒辣椒辣椒可产生称为辣椒素的辛辣防御化合物，包括辣椒素和二氢辣椒素，它们能对抗真菌病原体的生长。与其他微生物相比，从C. chacoense感染种子中分离出的真菌对这些辛辣化合物的耐受性更高，其生长速度有所降低，但并未完全被抑制。先前的研究表明，辣椒素类通过结合电子传输链（ETC）中的NADH脱氢酶破坏ATP的产生来抑制微生物，从而抑制氧化磷酸化（OXPHOS）。辣椒素也可能破坏细胞膜。在这里，我们调查分离自C. chacoense的真菌种子病原体中的辣椒素耐受性。我们从4个子囊藻属（链格孢菌，炭疽菌，镰刀菌和拟腐菌中选择了16种真菌分离物。）。使用相对生长速率作为耐受性的读数，使用ETC抑制剂对真菌进行攻击，以推断真菌是否具有其他呼吸酶，以及对ETC的作用是否充分解释了辣椒素的抑制作用。在所有分离物中，我们发现了至少一种替代NADH脱氢酶的证据。在许多分离物中，我们还发现了另一种氧化酶的证据。这些数据表明，野生植物病原体可能是替代呼吸酶的丰富来源。我们进一步证明了这些真菌分离物能够分解辣椒素。最后，我们确定OXPHOS理论可能描述了一种弱的主要机制，通过该机制，二氢辣椒素而不是辣椒素会减慢真菌的生长。我们的发现表明，除了能量中毒之外，辣椒素还可能破坏细胞膜，

重要事项植物会制造化合物来保护自己。例如，辣椒会产生辛辣的辣椒素，以抑制病原体的破坏和动物摄食。在人类中，辣椒素与膜通道蛋白结合，产生热感，而在微生物中，辣椒素通过结合呼吸酶来限制能量产生。但是，一些数据表明辣椒素也能破坏膜。在这里，我们研究了从野生辣椒辣椒（辣椒）中分离出的真菌病原体（链格孢属，炭疽菌，镰刀菌和拟南芥）。。通过在存在已知呼吸道靶标的抗生素存在下测量生长速率，我们推断野生植物病原体可能富含其他呼吸道酶。菌落周围的清除区以及液相色谱-质谱分析数据进一步表明，这些真菌可以分解辣椒素。最后，辣椒素对呼吸酶的总抑制作用尚未完全解释。我们的发现为辣椒素可能破坏细胞膜，对微生物学以及人类健康产生影响的研究提供了依据。